A decadodecasil-3R (DDR) zeolite has an internal pore size of 0.36×0.44 nm2, such that the DDR zeolites may serve as a molecular sieve through which CO2 having a size of 0.33 nm does not pass but N2 having a slightly larger size of 0.364 nm may pass. However, although existing DDR zeolite membranes reported in documents based on the molecular sieve as described above have high separation performance with respect to a CO2/N2 mixture, in the case of preparing a DDR zeolite membrane using 1-adamantanamine (ADA) which is well-known structure-directing agent, (SDA) it is difficult to secure high performance. It may be judged that a sufficiently continuous membrane was prepared through scanning electron microscopy, but actually, CO2/N2 separation performance of the membrane is significantly low. It may be confirmed through experiments that it is very challenging to prepare a DDR zeolite membrane having high performance using the existing structure-directing agent, ADA. However, it is judged that when the DDR zeolite membrane is prepared without defects, it is possible to provide a competitive separation process as compared to other CO2 separation technologies (absorption/adsorption, and the like).
Since DDR zeolite may be prepared in a form in which a Si fraction is high, ingredients thereof are mostly SiO2, thereby exhibiting hydrophobicity. In a case of preparing a membrane using a general hydrophilic zeolite (for example, SAPO-34 (chabazite structure; CHA), NaY (faujasite structure; FAU), or the like), the membrane exhibits high CO2/N2 separation performance. High CO2/N2 separation performance is generally resulted from close interaction between CO2 and SAPO-34 having hydrophobicity. However, when moisture is present together with CO2/N2, CO2/N2 separation performance may be deteriorated. In order to decrease energy, it is essential to secure technological skills capable of exhibiting high CO2/N2 separation performance without an additional process for removing moisture even though moisture (at most 10%) is present in flue gas.
In a case of a hydrophilic chabazite type zeolite membrane, CO2/N2 separation performance under a dry or wet condition and changes in separation performance depending on the presence or absence of moisture may be confirmed in a document (Li, S. G. & Fan, C. Q. High-Flux SAPO-34 Membrane for CO2/N2 Separation Ind. Eng. Chem. Res., 2010, 49(9), 4399-4404).
Further, in a case of a hydrophilic faujastite (FAU) membrane, CO2/N2 separation performance under a dry or wet condition and changes in separation performance depending on the presence or absence of moisture may be confirmed in a document (Gu, X. H., et al., Synthesis of Defect-Free FAU-Type zeolite Membranes and Separation for Dry and Moist CO2/N-2 Mixtures Ind. Eng. Chem. Res., 2005, 44(4), 937-944).
A secondary growth method of hydrothermally synthesizing a seed layer using 1-adamantanamine (1-ADA), a conventional organic template, in a method of preparing a DDR zeolite membrane has disclosed in U.S. Patent Application Publication No. 2013/0064747A1. However, the ADA organic template has a problem in that it is significantly difficult to effectively prepare a continuous membrane.
Tomita et al., disclosed a method of preparing a DDR zeolite membrane by hydrothermally synthesizing a seed layer made of DDR zeolite particles using the ADA organic template, similarly in U.S. Patent Application Publication No. 2013/0064747A1 (Tomita et al, Microporous and Mesoporous Materials 68 (2004) 71-75).
Himeno et al. disclosed a method of preparing a DDR zeolite membrane by hydrothermally synthesizing a seed layer made of DDR zeolite particles using the ADA organic template in the same manner as in the above-mentioned documents (Himeno et al., Industrial & Engineering Chemistry Research 46 (2007) 6989-6997).
Meanwhile, up to now, in a post-combustion carbon capturing process using a membrane, a hydrophilic zeolite (for example, NaY zeolite) selectively adsorbing CO2 has been generally used as a material of the membrane. However, since water vapor (at most 10%) is contained in flue gas discharged from coal-fired power plants, CO2 selectivity of the hydrophilic zeolite membrane having high selectivity under a dry condition is significantly decreased under a wet condition. Since water vapor has a molecular size (0.265 nm) smaller than a size (0.33 nm) of CO2, it is impossible to selectively separate only CO2 through the membrane. In this case, it is a wise approach to allow water vapor not to permeate through a membrane as much as possible using a hydrophobic membrane material.
Further, DDR zeolite membranes reported up to now have a random orientation in which a pore structure is not aligned in any one direction, but is randomly aligned in an out-of-plane direction. In this case, there is a problem in that a permeation rate of CO2 passing through the membrane is decreased, such that in a case of treating the same volume, a larger amount of membrane is required as compared to a membrane having a rapid permeation rate.
Therefore, the present inventors tried to solve the above-mentioned problems and confirmed that a continuous membrane in which pore structures in hydrophobic DDR zeolites having a continuous out-of-plane orientation are aligned may be prepared with high reproducibility as compared to an ADA organic template according to the related art by hydrothermally synthesizing a substrate on which a seed layer is formed using a silica source synthetic precursor containing methyltropinium cations, and the above-mentioned hydrophobic DDR zeolite membrane having the out-of-plane orientation exhibited high CO2/N2 separation performance even in a situation in which moisture is present, thereby completing the present invention.